Layer system

Abstract

A system for bonding layers ( 1 ) of different chemical compositions, such as bonding a thermal barrier layer to a metal substrate on a surface of a gas turbine component. A substrate ( 4 ) made either of a ceramic material or particularly of a metal super-alloy may be bonded to an outer layer ( 16 ) such as a ceramic by means of a fine-grained intermediate layer ( 7 ) bonded to the substrate ( 4 ), and a coarse-grained layer ( 10 ) bonded to the intermediate layer ( 7 ) to create a studded surface ( 9 ). The fine and coarse layers ( 7, 10 ) provide a transition between the substrate ( 4 ) and the outer layer ( 16 ) for improved bonding between them. The studded surface ( 9 ) may provide at least a 20% increase in bonding surface area for the outer layer ( 16 ). Additionally, a medium-grained layer ( 13 ) may be applied to the studded surface ( 9 ) before applying the outer layer( 16 ).

1. A layer system, comprising:
 a substrate comprising an outer surface; 
 an intermediate layer comprising a composition of MCrAlY at least partly comprising grain diameters less than 22 micrometers, the intermediate layer applied to the outer surface of the substrate; 
 a coarse-grained layer comprising a composition of MCrAlY with particle diameters greater than 80 micrometers, the coarse-grained layer applied as substantially a single layer of particles on the fine-grained layer, forming a studded bonding surface with at least 20% more surface area than the outer surface of the substrate; and 
 an outer ceramic layer applied to the studded bonding surface; 
 wherein the M in MCrAlY represents an element selected from the group consisting of iron, cobalt, and nickel. 
 
     
     
       2. The layer system as claimed in  claim 1 , wherein a further layer between 40 and 80 micrometers thick comprising a composition of MCrAlY with a mean grain diameter between 22 and 62 micrometers, is sprayed onto the studded bonding surface prior to the application of the outer layer, wherein the M in MCrAlY represents an element selected from the group consisting of iron, cobalt, and nickel. 
     
     
       3. The layer system as claimed in  claim 1 , wherein approximately 50% of the grain diameters in the intermediate layer are between 8 and 22 micrometers. 
     
     
       4. The layer system as claimed in  claim 1 , wherein the intermediate layer is dense. 
     
     
       5. The layer system as claimed in  claim 1 , wherein the substrate is a cobalt- or nickel-based superalloy. 
     
     
       6. The layer system as claimed in  claim 1 , wherein the outer layer is a thermal barrier coating. 
     
     
       7. The layer system as claimed in  claim 1 , wherein the intermediate layer is applied by plasma spraying. 
     
     
       8. The layer system as claimed in  claim 1 , wherein the layer system is a gas turbine part. 
     
     
       9. The layer system as claimed in  claim 1 , wherein the particles have diameters greater than 100 micrometers. 
     
     
       10. A method of forming a layered wall of a gas turbine component, the method comprising:
 applying an intermediate layer of MCrAlY comprising a grain size distribution between 8 and 44 micrometers to an outer surface of a metallic substrate; 
 applying a substantially single layer of MCrAlY particles greater than 80 micrometers in diameter to the intermediate layer, forming a particle-studded bonding surface on the intermediate layer with at least 20% greater surface area than the outer surface of the substrate; 
 and applying a ceramic thermal barrier layer to the particle-studded bonding surface; 
 wherein the M in MCrAlY represents an element selected from the group consisting of iron, cobalt, and nickel. 
 
     
     
       11. The method of  claim 10 , wherein approximately half of the grain sizes in the intermediate layer grain size distribution are less than 22 micrometers. 
     
     
       12. The method of  claim 10 , wherein the substantially single layer of MCrAlY particles are applied to the intermediate layer by a plasma spray process that melts only a surface region of the particles to allow bonding of the particles to the intermediate layer. 
     
     
       13. The method of  claim 10 , wherein a surface portion of the intermediate layer is heated to a soft condition, and the MCrAlY particles are sprayed onto said surface portion of the intermediate layer at sufficient velocity that the MCrAlY particles penetrate into said surface portion of the intermediate layer, and are anchored therein. 
     
     
       14. The method of  claim 10 , further comprising applying a spray material comprising a mean grain size of 22-62 micrometers in a layer 40 to 80 micrometers thick on the particle-studded bonding surface prior to applying the ceramic thermal barrier layer thereto.